1) Field of the Invention
The invention relates to modular profiled wire flat screen panels which are adapted to be mounted on a screen deck support assembly to classify materials, and particularly to arrangements for mounting said panels so they can be used in a vibrating apparatus. The screen panels typically comprise a plurality of parallel stainless steel profiled wires which are each welded to an underlying series of spaced apart support rods positioned normal to the wires.
2) Description of the Related Art
A principal use for such panels is in coal processing plants where the smaller particles in the crushed coal which is processed over the screens passes through the slot openings. In many cases the screens will be arranged so that the coal will pass from one screen deck to another, which is either in line with it or under it. By having larger slot openings in the first or upper deck, a greater volume of coal can be processed. This is true since the second deck, which has smaller slot openings, and thus a lower capacity, will only have to contend with processing those particles which have passed through the larger slots of the first deck. Depending upon the hardness and tonnage of the material being processed, the screen decks will have their screen slots gradually enlarged and will start to wear thin from abrasion in a relatively short period of time, sometimes in as little as two weeks or so. Since prior art screen deck systems often require a crew of 2-4 people working many hours to remove the worn screen panels and replace them with new ones, it is obvious that a system which allows panels to be replaced quickly will offer tremendous cost savings, not only in labor but in lost processing time.
One example of a prior art system is that disclosed in Tabor U.S. Pat. No. 4,909,929 wherein a plurality of modular panels are retained by longitudinally extending retainer bars made of a resilient material such as urethane. The retainer bars have somewhat semi-spherical sockets formed in their top and one side surface in such a manner that when two retainer bars are placed side-by-side in abutting relation on top of a support member on the machine, they form a somewhat spherical socket which has an integral tapered bottom portion extending well below the flat bottom surface of the retainer bar. The integral tapered bottom portions are spaced at uniform intervals, such as 10 cm, which correspond to the spacing of a plurality of holes formed in the support members of the screen deck. As a pair of retainer bars are laid side by side on top of the support members, the tapered bottom portions will extend through the holes in the underlying support members. Locking pins may then be driven down into the centers of the sockets. Since the bottom portion of each locking pin is larger in diameter than the inner diameter of a tapered hole formed in the bottom of the tapered bottom portion, the walls of the tapered bottom portion will be forced radially outwardly from the vertical plane where the two retainer bars abut each other. This radially outward movement will cause the distance between the outer walls of the tapered bottom portions, as measured in a vertical plane normal to the plane of abutment, to be greater than the diameter of the holes in the support members. Thus, the retainer bars will be held in contact with the support members and prevented from moving upwardly relative to said support members. Although this design is effective in retaining screen panels, it has been found that a great deal of time must be spent when screen panels are to be replaced. For example, in commercial applications of the design, the upper ends of the locking pins are protected by elongated overlying cover strips which have spaced portions which engage with the retaining ridges formed at the top of each socket. Since the cover strips are very difficult to remove, the standard practice has been to drill through the cover strip at the location of each pin. This can be a very tedious operation, and especially so when multi-layer deck assemblies have one deck located just 60 cm or so below another deck. Since the tapered bottom portions which enter the holes in the support members are integral with the retainer bars, they are not able to accommodate substantial increases in the diameter of the holes in the support members which can take place due to wear over long periods of time. Also, although the holes in the support members tend to engage the outer surfaces of the abutting pairs of tapered bottom portions and hold them together, wear of the holes will allow the abutting walls of the retaining bars to move apart. They can also move apart because they are made of an elastomeric material which will be compressed against the sides of the openings in the support bars as the locking pins are driven into the sockets. Obviously, any separation of the retaining bars will close up the space between sets of retaining bars which is available for the placement of replacement screen panels. This situation usually means that all of the panels must be replaced at once, and arranged in place before the locking pins are placed in any of them, even though only some are worn.
Another prior art system has been sold under the name "Pro-Deck". This system also uses sets of resilient retaining bars which have recesses in one side wall which cooperate with identical recesses on an adjacent bar to provide a plurality of socket-like recesses into which resilient, generally cylindrical sleeves can be placed. The bottom surfaces of the retaining bars are flat and are positioned so as to overlie the support member. The generally cylindrical sleeves are complementary in shape to the aligned recesses in the sets of retaining bars and elongated so they will extend through and beyond the spaced apart holes in the underlying support member. To accommodate wear of the holes in the support member, replacement sleeves can be used in which the lower end portions of the sleeves have larger diameters. The lower end portions of the sleeves have a tapered internal opening and a vertical slot which allows the side walls to expand radially outwardly away from each other as the locking pin is forced downwardly. Since each set of retaining bars is held only against vertical movement by the sleeves and lockpins, it is possible for the abutting side walls of the retaining bars to become slightly spaced from each other, thus presenting the same problem in replacing individual screens as previously described.